Question: Simplify the following expression: $r = \dfrac{3}{7x - 9} \div \dfrac{4}{10x}$
Answer: Dividing by an expression is the same as multiplying by its inverse. $r = \dfrac{3}{7x - 9} \times \dfrac{10x}{4}$ When multiplying fractions, we multiply the numerators and the denominators. $r = \dfrac{ 3 \times 10x } { (7x - 9) \times 4}$ $r = \dfrac{30x}{28x - 36}$ Simplify: $r = \dfrac{15x}{14x - 18}$